An RF circulator is a device with n ports allowing an RF signal to circulate in a single direction. Consideration is given to a circulator with three ports p1, p2, p3. A signal injected into a port p1 is transmitted to the port p2 and insulated from the port p3, while a signal entering via the port p2 is transmitted to the port p3 and insulated from the port p1. This therefore gives a decoupling of the transmitted and received signals. A symbolic illustration corresponding to such a circulator the port p2 of which is connected to an antenna is given in FIGS. 1a and 1b. If the circulator receives a radio frequency signal on the impedance-matched port p1, this gives a low insertion loss path in the clockwise direction and great losses are observed in the opposite direction. The power is therefore directed virtually without loss to the port p2 and radiated by the antenna. The same thing applies from the port p2 to the port p3, and from the port p3 to the port p1. In this way the circulator has essential qualities of transmitting without loss in a given direction and of very greatly attenuating the reflected waves.
Circulators are notably used in telecommunication or radar systems according to the principle illustrated in FIG. 2. FIG. 2 illustrates schematically an example of a system for transmitting and receiving electromagnetic signals for applications notably of the radar type, normally called a T/R module consisting essentially of three stages as described below.
The first stage, the core of the CA system, serves to manage and process the signals received and transmitted. The second stage consists of power amplifier elements. These elements are divided into two functionalities, the high power amplifier normally called HPA, 11 which serves to give power to the signal leaving the first stage in order to be transmitted by the antenna and the low noise amplifier normally called LNA, 16 which serves to amplify the power of the signal received by the antenna while limiting interference to the maximum. These two components are extremely sensitive to the power received by the antenna: the LNA because the power that enters the latter must not exceed a certain threshold without which the component is damaged and destroyed; the HPA because it is always connected with a loopback to the output and must in no circumstances receive power on its output if the user does not wish to damage or even destroy it. It is for this reason that there are, in the third stage, elements called limiters 12 and 15 which are electronic components the function of which is to cut the microwave signal if the power of the latter exceeds a certain threshold. Also found in this third stage are elements called circulators 13 and 14. These are components called active components which direct an incoming stream to an output specific to the input used. For example, from the port 1 to the port 2, from the port 2 to the port 3 etc. hence the name of circulator. This physically means that irrespective of the impedance of the output circuit, there is practically no return to the input of the circulator. If there has to be a reflection, the energy is considered to be an incoming stream via the first output and is therefore directed to the next output, almost perfectly insulating the input.
Currently this type of transmit/receive system comprises ferromagnetic-material-based circulators and diode-based limiters.
The existing defects are mainly:                the high cost of these components which are not easily reproducible because they require human intervention to be correctly set;        the losses generated by these components of the order of 4 to 8 dB in their frequency band which is itself very narrow (0.2 to 2 GHz) for the circulators and of the order of 1 dB for the diode-based power limiters.        
These components currently occupy 80% of the space in a telecommunication system and are an additional obstacle to miniaturization. Since the circulators currently employed are ferrite-based components, they are by nature active components and consume energy; they are also very bulky (of the order of 70% of the weight relative to the volume of the T/R module) and because they are difficult to reproduce are very expensive.
The diodes for their part are components that have considerable costs and the losses generated by these components are in the order of 1 dB. Furthermore, the diodes occupy a considerable proportion of the space in the telecommunication systems and thereby represent an additional obstacle to miniaturization.
It has already been proposed in the prior art to use microwave microswitches also called RF MEMS switches. They are microdevices of the capacitive type operating like switches, microdevices that are called microswitches in the rest of the description.
The microswitches of the capacitive type are particularly valued in microwave applications, notably for their low response time allied with not very high control voltages ranging from a few volts to a few tens of volts. Advantageously they are very small, of millimetric size (2 to 10 mm2), that is on average ten times smaller than a ferromagnetic circulator and much lighter. They consume very little. They are not very costly to produce because they use the manufacturing techniques that are usual in microelectronics, from a substrate that is usually made of silicon, and are very easy to reproduce. Their insertion losses are very low, usually in the order of 0.1 to 0.2 dB over a very wide frequency band, 18 to 19 GigaHertz. More precisely, in this solution, serial microswitches are proposed: one input signal line and one output signal line in the extension of one another, separated by a switching zone, and electrically insulated, and, above the switching zone, a flexible membrane resting on pillars. The switching zone is covered with a dielectric. The membrane is either in the rest position, up, the capacity formed by the switching zone, the dielectric and the membrane having a low Coff value, so that the two signal lines are insulated, either in the low position so that both portions of line are coupled in a capacitive manner, the capacity formed by the switching zone, the dielectric and the membrane having a high Con value, allowing the transmission of a radio frequency or microwave signal. The control of the membrane is a voltage control applied in an appropriate manner in the switching zone, the membrane being taken to a reference potential (electric ground) by the pillars. The switching performance (transmission, insulation) depends notably on the Con to Coff ratio which must be as high as possible.
The circulator comprises at least one first and one second contact pads in order to apply the control voltages in the on or off state on at least one of the portions of the control electrode of the first microswitch and of the second microswitch. The activation voltages are in the order of from one volt to a few tens of volts. The microswitches may be controlled simultaneously in the off state or one in the on state and the other in the off state.